How Corporate Proxies Decrypt Your HTTPS Traffic Using TLS Interception

TLS interception, also marketed as SSL inspection or HTTPS filtering, is a widely used feature in enterprise firewalls and secure web gateways that allows organizations to decrypt and re-encrypt employee web traffic. It works by installing a custom root certificate authority on managed devices, enabling a proxy to silently sit between the user and the destination website, reading all data in plaintext. While organizations justify the practice as a malware-scanning measure, a 2017 study by researchers from Mozilla, Google, and Cloudflare found that most intercepting middleboxes negotiated weaker encryption than the original client would have. The findings were serious enough for US-CERT to issue an alert that same year warning that HTTPS inspection tools could undermine the very protections TLS is designed to provide. The technique does not break encryption but effectively relocates the endpoint, meaning sensitive data such as passwords and private messages is fully visible to the proxy.